Carbon dioxide atmosphere modifiers for packaging

ABSTRACT

A device or sachet ( 3 ) for maintaining or modifying the atmosphere in a package suitable for meat, beef, lamb, pork, etc. the device including at least two containing layers ( 4, 5 ), a moisture activated chemical substance ( 6 ) contained by the containing layers, and at least one absorbent layer ( 7 ). Moisture within the package is soaked up by the absorbing layer. The moisture is then transferred from the absorbing layer to permeate through a micro-porous layer ( 5 ) as water vapor and activate the chemicals. The gas produced by the chemicals then passes through the sachet and into the package&#39;s atmosphere. This modifies the atomosphere to ensure that there is an adequate quantity of CO 2  for achieving the desired shelf life of the packaged food.

TECHNICAL FIELD

This invention relates to methods and apparatus used in packaging. Moreparticularly, the principles of the present invention relate to thepackaging of food products such as meat using atmosphere modifiers.

Reference to the packaging of meat should not be seen to be limited asthe principles of the present invention may be equally applied to thepackaging of other food products.

BACKGROUND ART

The export and domestic consumption of meat, such as beef, lamb, chickenand other meats, provides a significant source of revenue for manycountries. It is therefore important that this product arrives at itsdestination having the highest possible quality. It therefore followsthat packaging methods used to contain the meat in transit must be ofhigh quality in order to keep the meat in a desired state.

There are however problems with the current methods and apparatus usedto package meat.

A natural process that must be mitigated or avoided, is oxidation. Thisoccurs by oxygen coming in contact with the meat during storage andtransit, causing oxidation.

In general, consumers perceive that meat coloured red is fresh, andtherefore preferable to discoloured meat. However, storage underconditions where oxygen is present results in gradual browning of themeat. While in many cases the product is still acceptable forconsumption, consumers are deterred by the brownish appearance of themeat which they associate with a spoiled product.

In cases where long-term storage of meat is necessary, the presence ofoxygen can result in spoilage of the meat in addition to the browning ofthe meat.

One method of avoiding oxygen spoilage, is vacuum packaging the meat inan oxygen impermeable barrier film. The problems associated with thisare that the meat, under a low or nil oxygen modified atmosphere or avacuum atmosphere, tends to develop a purple colouration which consumersfind unacceptable.

High oxygen/CO₂ modified atmosphere systems are successfully used forretail cuts of red meat, but the storage life is relatively low due toloss of colour.

A well known packaging system known as low oxygen/CO₂ packaging is incurrent use however has been mainly directed to non-retail readymarkets.

The shelf life of CO₂ packaged meat is longer than for vacuum packedmeat. The meat stored under CO₂ will rebloom on exposure to oxygen,giving the red colouration which consumers associate with freshness.

The display life of CO₂ packaged meat, in the oxygenated state appearsto be longer than that of vacuum packed meat. This may be attributed tothe low oxygen concentration throughout the product lifetime.

The use of low oxygen/high CO₂ packaging is well known, as is the use ofoxygen absorbing compositions with meat products.

CO₂ will be absorbed in significant quantities by the meat within thefirst 48 hours of exposure. This absorption causes the internal pressureof the package to be reduced, unless there is a sufficient excess of CO₂to saturate the meat, and a suitable mechanism by which the volume ofthe package may contract.

Therefore if the meat is placed on a conventional sized tray, evacuated,gas flushed with CO₂ and then sealed under a barrier film, severedistortion will occur as the CO₂ is absorbed and the internal pressureof the system is reduced. This is because the volume of the rigid traycannot contract in a controlled manner like that of a bag, and becauseinsufficient CO₂ is present to compensate for that which is absorbed bythe meat.

This effect may be reduced if a high package volume in relation to thevolume of the product is achieved. However this is undesirable toconsumers and results in excessive packaging and waste.

One solution to the above problems has been to provide a sachet of asubstance that absorbs oxygen and releases CO₂ in response to humidity.The sachet may be placed between one gas permeable layer immediatelysurrounding the meat, and a second gas impermeable layer.

In some embodiments, the sachet is placed over a hole in the permeablelayer. This allows activation by in-pack humidity. The holes also allowsrapid equilibration of gases. This embodiment thus produces a modifiedatmosphere package whereby distortion, excess oxygen and theirassociated negative effects is reduced.

Although this process has been successful, there have been problemsassociated with it.

Due to a number of steps that must be undertaken to implement the systemfor packaging the meat, the packaging process is complicated andexpensive. For example, the process must be made accurate enough so thatthe sachet containing the regulating chemicals is placed over the holein the permeable layer. An absorbing layer must also be placed in thepackage between the meat and the bottom of the package in order toabsorb the fluids that may exude from the meat. The supermarkets place apricing or use by date label over the hole once the sachet is removed,to avoid leakage and prevent contamination.

Other methods of atmosphere modification are desiccant sachets, sulfurdioxide emitters and devices for liberating chlorine dioxide.

These, combined with oxygen absorbers, and combined oxygen absorber/CO₂generators form part of the technology known as active packaging.

Sachets that contain a CO₂ liberating chemical substance may be used inactive packaging. This sachet may be made from a micro-porous,non-permeable membrane that allows transfer of humidity, but does notallow the transfer of liquid through the membrane.

There is also a need to transfer humidity from the pack to the sachet inorder to initiate the atmosphere regulating chemicals. European PatentEP0128795 describes oxygen or CO₂ generators housed in sub-compartmentsof packages. The chemicals react on contacting the drip from the meat.No microporous films are used.

French Patent 2 621 015, describes CO₂ releasing chemicals, which aredistributed in a fibrous structure. The hydro-phobicity of the fibresprevents the chemicals from leaching into the food.

European Patent EP0 468 880 A1, describes oxygen absorbers and/or CO₂generators housed in liquid impermeable vapour permeable packets. Thepackets have two compartments housing the reactive components linked bya weak seal. Rupture of the weak seal causes the two components toreact, thus modifying the package atmosphere.

All of the above documents describe devices that suffer the problem ofrequiring moisture vapour to activate the compounds, wherein the vapouris not drawn around or local to the sachet to sufficiently activate thecompounds in the sachet.

What is needed then is a system of modifying the atmosphere of a closedpackage, by a

process that is uncomplicated and does not necessitate the stepspreviously used.

It is an object of the present invention to address the foregoingproblems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will becomeapparent from the ensuing description which is given by way of exampleonly.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided adevice for maintaining or modifying the atmosphere in a package, thedevice including:

at least two containing layers,

a moisture activated chemical substance contained by the containinglayers,

and at least one absorbent layer attached to at least one of thecontaining layers.

The present invention also relates to a method of packagingcharacterised by the step of placing into a package a device asdescribed immediately above.

The absorbent layer may be any device capable of retaining and/orabsorbing and/or transferring liquid or humidity.

The absorbent layer may be any suitable material, but preferably offood-grade quality.

The absorbent layer may contain a cellulosic absorbent such as paper orwood pulp or viscose fibers, superabsorbent polymers and the like and ispreferably heat sealed to the adjoining layer.

Preferably the absorbent layer is of a thickness and type to absorb allof the fluid released by the product.

A preferred feature of the present invention is to have the absorbentlayer of sufficient type and thickness to absorb excess fluid from theproduct or pooling in the tray packaging.

The absorbent layer may be attached to the containing layers by manymeans and in one embodiment may be heat sealed to the containing layer.

Reference to packaging will now be made with reference to the packagingof meat in a plastic container. This should not be seen to be limiting,as the principles of the present invention may be applied to thepackaging of other substances and containers of other types.

Preferably the plastic container will include a substantially rigid basewith plastic films at the top. The base may also include ribbedportions.

Reference to a rigid base and plastic top should not be seen to belimiting the scope of the present invention's, manufacture or use, asother container configurations may be used without departing from thescope of the present invention.

These atmosphere modifying absorbent pads may be used in non-retailpacks such as in vacuum packed meat primal cuts or alternatively in bulkgas flushed packages.

In preferred embodiments there are two containing layers. Preferably,one of the containing layers positioned next to the absorbing layer isformed from a micro-porous film. Micro-porous films have high moisturevapour transmission rates (MVTR'S) and are not permeable to liquidwater. These high MVTR materials allow water vapour to rapidly activatethe chemical contained between the layers, but do not allow thechemicals to leach out and contaminate the foodstuff

Because of the nature of these films, it is preferable that the productdoes not come into contact with the micro-porous film as localdessication can occur. Therefore it is envisioned that in use the deviceis placed in the packaging with the product on top of the containinglayer (external) which is not micro-porous.

Reference to the present invention may now be made by reference to asachet. Reference to a sachet should not be seen to be limiting thescope of the present inventions manufacture or use.

In one example, one side of the sachet may be constructed from a PETlaminate or similar heat resistance material, and the other side fromthe micro-porous film.

Thus, it can be seen that the preferred structure of the presentinvention has an absorbent layer positioned on the bottom of the packagewhich is next to a micro-porous layer that transfers moisture vapor fromthe absorbent layer or the humid atmosphere of the package to chemicalscontained by the micro-porous layer and the other containing layer. Thenon-micro-porous containing layer ensures that there is no localdesiccation of the product on top of it and both the containing layersensure that the chemicals do not come into contact with the product.

Preferably the absorbing layer is peripherally bonded to the othercontaining layer. In some embodiments the peripheral bonds are heatlaminated bonds or formed by heat lamination.

In one embodiment one or more containing layers may have oxygenabsorbing capabilities.

In one preferred embodiment, the chemicals in the present invention maybe one or a combination of moisture activated chemicals that modify theatmosphere to the desired configuration.

Preferably, the quantity and configuration of the chemical will bechosen for the appropriate expected shelf life and storage length of theproduct packaged.

The chemical may be a system capable of evolving or removing CO₂ over aperiod of time. This should not be seen to be limiting however. Forexample, in other preferred embodiments the chemical may remove oxygenfrom or release oxygen to the environment of the package. Anti-microbialgases may also be released from the chemical.

The present invention has a number of advantages.

A number of humidity triggered atmosphere modifying devices are knownand are used in food packaging. These include sachets which absorboxygen, absorb oxygen and generate CO₂ and those which generatecarbon-dioxide only. These chemicals must be kept separate from the foodusing a functional barrier. The present invention achieves this by theuse of the micro-porous film which only allows transmission of allgases. For example, these may be water vapour, CO₂ gas, oxygen and soforth. This list should not be seen to be limiting.

The presence of the absorbing device in the present invention ensuresthat sufficient moisture vapor is transferred to activate the chemicalsthat control the modified atmosphere. This combination of absorbentlayer and containing layers, one of which is micro-porous, addresses theproblems associated with the prior art.

In many cases where the absorbing layer is not present, and the meat orfoodstuff does not contain sufficient moisture, the moisture activatedatmosphere modifying chemicals are not activated sufficiently to modifythe atmosphere to the required specification. The present inventionavoids this possibility by providing the absorbing layer that containsmoisture that may be transmitted over a period of time thus activatingthe desired chemicals allowing the gases evolved to pass through themicro-porous film into the package.

It is preferable to have the chemicals activated slowly over a period oftime to prevent over-inflation of the package and possible rupture ofthe seal.

The present invention also has the advantage of acting as a dripabsorbent in the final package. Thus, there is not the problem of liquidforming on the bottom of a package and spilling on an undesired locationwhen the package is opened. Thus, the present invention has theadvantage that it may be used as a drip absorber as well as anatmosphere modifier.

Thus, one device can absorb excess fluid, modify the package atmosphere,and eliminate problems associated with prior art atmosphere modifiers.

In preferred embodiments, these atmosphere modifying devices may be usedin a sheet form between layers of modified atmosphere packagedfoodstuffs to ensure there is no concentration gradient of gas throughthe sample.

The present invention describes an absorbent pad which contains a fluidimpermeable gas permeable section containing atmosphere modifyingchemicals. These chemicals are formulated to either generate CO₂ or togenerate CO₂ and absorb oxygen.

The structure may also be used to house other atmosphere modifyingchemicals when the product produces liquids. The chemicals need to bephysically separated from the product. The reaction of these chemicalsis triggered by the humidity of the product. The present invention hasthe advantage of keeping the chemicals separate from the food thuspreventing them from leaching out of the sachet.

The present invention may be particularly useful in modified atmospherepackages and in conjunction with evacuation/gas flushing.

Some examples of the present invention are described below.

EXAMPLE 1

An absorbent pad capable of generating carbon dioxide and absorbingoxygen was prepared with the following materials:

Layer 1 PET film adhesively laminated to high opacity filled PE film.

Layer 2 Microporous polypropylene film with Gurley Air permeability of100 sec/100 cc.

Layer 3 Non woven fabric consisting of a mixture of viscose fibres andpolypropylene fibres with a weight of 120g/m².

A fine particle size well mixed powder of the following composition byweight was prepared:

Sodium bicarbonate 472.28 Fumaric acid 280.2 Sodium erythorbate 67.33Ferrous sulphate 39.6 Calcium chloride 130.7 Fumed silica 9.9

1.75 g of the formulation was placed in between layers 1 and 2 asdescribed above to form a cell of dimensions 58×56 mm. A high speedfilling machine of proprietary design was used.

The absorbent pads were sealed in a barrier pouch and held at chilltemperatures where they were stable to premature reaction for manymonths.

The pads were used to prepare long shelf life packages of beef, lamb andpork.

In barrier trays of volume 800 cc was placed two attached cells asdescribed above. The cells were placed so that the PET layer contactedthe meat, and the absorbent layer contacted the bottom of the trays. 500g of beef, pork or lamb was then placed in the trays, which were thengas flushed with a mixture of 80% carbon dioxide and 20% nitrogen. Theinitial oxygen concentration was less than 1000 ppm. The barrier liddingfilm used was a proprietary film produced by Cryovac Sealed AirCorporation, which can be delaminated at the point of sale to leave ahighly oxygen permeable film attached to the tray, and is described inU.S. Ser. No. 08/764,405 filed 11 December as a CIP application of U.S.Pat. No. 5,6861,126 which is incorporated by reference herein.

After 10 weeks storage at −1° C. the film was delaminated leaving theoxygen permeable film adhered to the tray. The products still have anacceptable retail display life in the oxygenated state. The bacterialevels were very low. For beef the initial counts were 2.7 log cfu/cm²which decreased to 2 log cfu/cm² after ten weeks at −1° C. After retaildisplay the total counts were 3.9 log cfu/cm² for samples stored for 1day before display, while samples stored for 10 weeks before display hada total count of 6.4 log cfu/cm² after retail display.

The packs showed no deformation due to carbon dioxide absorption, norexcess pressure caused by the presence of excess gas. No drip wasvisible in any of the packages at any point in the experiment.

There was no leaching of the chemicals from within the pad.

In further tests the pads could be suspended in water at 40° C. for manydays without leaching. Eventually the bond between the PET laminate andthe microporous film would break due to the pressure of water which hadentered the area containing the chemicals.

This experiment demonstrates the following:

These atmosphere modifying chemicals may be successfully used as part ofa drip absorbent system.

The chemicals are retained within the pouch after extended storageperiods.

The chemicals contribute to the drip absorbing function of the non wovenfabric by means of vapour transfer.

EXAMPLE 2

An absorbent pad capable of generating carbon dioxide, but not ofabsorbing oxygen was constructed as follows:

Sodium bicarbonate 550 Fumaric acid 320 Calcium chloride 130 Fumedsilica 10

The mixture was used to formulate a pad for packaging chicken portions.

EXAMPLE 3

A powder of the following formulation was prepared:

Iron powder 100 Sodium chloride 5 Precipitated silica 5

1 g of the powder was placed in between layers 1 and 2 in a structureidentical to that described in example 1.

The absorbent pad was placed in the bottom of the tray as in example 1and used to pack 500 g of beef. The tray was gas flushed with 100%nitrogen.

The scavenging sachet maintained an oxygen concentration of less than100 ppm throughout the lifetime of the package.

EXAMPLE 4

An absorbent pad was prepared as in example 1 except that Layer 3 wassubstituted with a material containing the following components:

Super absorbent fibres

Viscose fibres

Polyethylene fibres

The composite had a weight of 150g/m².

In a standard test using a 0.9% saline solution to compare theabsorption capacities the composite fabric absorbed 3500 g/m² of fluidversus 1500 g/m² for the fabric described in Example 1. This materialcould therefore be used in applications where much higher levels of dripare produced. The activity in terms of gas absorption and release werevery similar to that obtained in example 1.

EXAMPLE 5

Sulphur dioxide releasing absorbent pads may be prepared using thestructure described in example 1.

PCT/AU93/00562 describes a range of applications and materials which maybe used to release sulfur dioxide in a controlled and sustained manner.These sulfur dioxide emitting materials may be utilised in the presentinvention.

The pad has the dual function of absorbing fluids and releasing anantimicrobial gas, whilst effectively separating the chemicals from theproduct.

EXAMPLE 7

Oxygen releasing pads may be prepared by utilising sodium perborate orpercarbonate and the like compounds and mixtures in the cavity betweenLayers 1 and 2 of the structure as described in Example 1.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from thefollowing description which is given by way of example only and withreference to the accompanying drawings in which:

FIG. 1 shows a representation of one preferred embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIG. 1 there is shown a package, shown by arrow 1.

Package 1 includes a container 2, a sachet 3.

The sachet 3 includes containing layers 4 and 5 which hold a chemical 6.Layer 5 is micro-porous in nature, allowing vapour to pass through it,but not allowing any liquid or solid material to pass through the layer.

The chemicals modify the atmosphere in the container. These may be a CO₂emitting substance, or a combination of a CO₂ generating/oxygen absorberor absorber or any atmosphere modifier which needs to be effectivelyseparated from the packaged product.

The sachet 3 also includes absorbing layer 7 which faces the base of thetray.

The product 8 within the package is meat.

The container 2, is sealed by two separate film layers 9 and 10.However, in alternative embodiments, a single plastic film may be usedor a peelable laminate.

In use, the sachet 3, may be placed in the container 2 with theabsorbing layer placed downwards, and the meat added.

The moisture within the package is soaked up by the absorbing layer 7.The moisture is then transferred from the absorbing layer 7 to permeatethrough the micro-porous layer 5 as water vapour and activate thechemicals 6. The gas produced by the chemicals 6 may then pass throughthe sachet 3 and into the package's atmosphere. This modifies theatmosphere to the desired requirements.

Thus, the required atmosphere is maintained, and the chemical mixture isactivated without the chemicals contacting the product.

Aspects of the present invention have been described by way of exampleand it should be appreciated that modifications and additions may bemade thereto without departing from the scope of the appended claims.

We claim:
 1. A sachet for maintaining or modifying the atmosphere in apackage, the sachet including: (A) a moisture vapor activated chemicalsubstance contained by two containing layers bonded together, and (B) atleast one moisture absorbent layer immediately adjacent to, and bondedto at least one of the containing layers wherein each said absorbentlayer is external, relative to the said containing layers and whereineach containing layer positioned adjacent to an absorbent layer isformed from microporous film.
 2. A device as claimed in claim 1 whereinone containing layer is not microporous.
 3. A device as claimed ineither claim 1 or claim 2 wherein one or more of the containing layershave oxygen absorbing capabilities.
 4. A device as claimed in claim 1 orclaim 2 wherein the device is capable of being used as a drip absorber.5. A device according to claim 1 or claim 2 in which the moisture vaporactivated chemical substance, when activated, modifies the gaseousatmosphere of the package.
 6. A device according to claim 1 or claim 2wherein the moisture vapor activated chemical substance, when activated,releases oxygen or carbon dioxide to, or removes oxygen or carbondioxide from, the atmosphere within the package.
 7. A device as claimedin claim 1 or claim 2 wherein the absorbing layer is peripherally bondedto the other containing layer.
 8. A device as claimed in claim 7 whereinthe peripheral bonds are heat laminated bonds or formed by heatlamination.
 9. A method of packaging characterized by the step ofincluding within a package a device as claimed in any one of claims 1 to2.
 10. A method of packaging as claimed in claim 9 characterized in thatthe absorbent layer of the device is placed downwards within the packagesuch that it does not contact the product contained within the package.11. A device as claimed in any one of claims 1 to 2, wherein themoisture absorbent layer comprises at least one member selected frompaper, wood pulp, viscose fiber, and superabsorbent polymer.